heating?

i have a radiator in the kitchen that does not work, i have put a new thermostat on and flushed it out, it works for 4 days then goes cold. I recently had a new raditator fitted in the lounge with bigger water pipes going to it. Would this effect the kitchen radiator which as has smaller micro piping? the original plummer who fitted new radiator in lounge says that this bigger piping would not effect the kitchen rad is this true?